Stress

Theory

Stress (σ) is defined as σ = F/A, with units Pa or MPa. Normal stress acts perpendicular to the surface; shear stress acts tangentially. Engineering stress uses original area A₀; true stress uses the instantaneous area. Stress is a second-rank tensor: in 3D, six independent components fully describe the state of stress at a point.

Application

All structural analysis begins with estimating stress distributions under service loads. Stress concentrations at holes, notches, and sharp corners amplify local stress by factor Kt (typically 2-4×), causing premature failure. In FDM, interlayer bonding creates planes of weakness perpendicular to Z; stresses in this direction must stay low.

Common mistakes

Stress cannot be measured directly: it is inferred from measured strains via E. Residual stress from rapid cooling during 3D printing adds to service stress and can trigger warping or delamination under no external load. FEA is essential for complex geometries.

Related terms: Strain, Young's Modulus, Shear Stress, Von Mises Stress, Residual Stress